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Solid state vs. Tube amp - Technical argument ?

Theodore8

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As a newbie trying to educate myself about speaker design, I fell upon the below (and attached) seemingly helpful document from Swiss manufacturer Jean Maurer:

https://www.jeanmaurerhifi.ch/annexes/catalogues/loudspeaker-technical-document.pdf

I was however taken aback by his arguing that tube amplifiers are superior to solid state because "taking up the electromotive counterforce (emcf) causes many problems for the outputs of direct transistor amplifiers, i.e. those without output transformers. The re-absorption of energy is poorly controlled, with all the consequences already mentioned above." (full quote on page 10).

Reading ASR, I assume the problem he identifies has been solved some time ago (cf. Benchmark, Constellation Hercules, UcD, Purifi Eigentakt... among others).

Could anyone on ASR with technical knowledge comment on this? Thank you.
 

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  • loudspeaker-technical-document.pdf
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fpitas

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A long long time ago (before 1970?), that *might* have been true. If that's a recent paper, he's come through a time-tunnel.
 

Jim Taylor

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This was posted at Parts Express Techtalk about 16 years ago. It may help you.

"My guess is you are being lead astray by B.S.
Back EMF is a concept you learn in the beginning stages of electronics.
It is used to explain how devices such as inductors, motors, speaker drivers or any electromagnetic device can impede the flow of electricity.
A motor, speaker or inductors coil may have given resistance but apply a given voltage and less current flows than ohms law would predict at certain times.
Current is slow to start in the inductor, when the speakers diaphragm moves it impedes the flow of current and same with the motors shaft.
The explanation is that the device generates it's own voltage in opposition to the applied voltage and that is why less current flows (because their is effectively less voltage applied to the circuit applied EMF - back EMF).
All fine and good.
That is the last you should hear or think about back EMF.
Moving on to the next level of electronics you move on to measuring impedance vs. frequency.
A motor operates at DC so you don't measure it's impedance vs. frequency but understand that it's impedance rises in proportion to it's shafts angular velocity.
An inductor has an impedance that increases with increasing frequency due to it's back EMF.
A speaker driver has an impedance curve with a resonant peak at Fs and rising impedance at high frequency due to voice coil inductance.
You probably have noticed that there are some 'experts' about who are trying to analyze a system by following the signal through a system from the amplifier through a crossover to the driver and following back EMF from the driver back to the amplifier.
This is the scientific equivalent to chasing your tail.
Any time you see someone attempting this you can immediately ignore them as they are talking of things way over their head.
To calculate how a driver interacts with a circuit and amplifier you measure its impedance and then solve the system as a circuit.
You can also model a driver rather than measure its impedance by substituting an equivilant circuit like this simplified one shown below and then solve the whole thing (you can get more detailed with your equivilant circuit depending upon your needs).
Impedance fully describes back EMF and separate consideration need not be given to back EMF.
In fact you cannot consider back EMF separately.
Back EMF has no place outside of beginning electronics.
Once you go beyond that you always use impedance vs. frequency.
So what you have is a drivers impedance and how the amplifier handles it.
Damping factor is a layman's term for output impedance.
The lower an amplifiers output impedance (higher damping factor) the less the output will be effected by varying load impedance.
Of course you have to remember that the loop impedance of your speaker wire adds to you amplifiers output impedance and is probably several times greater.
You want the combined output impedance of your amplifier and speaker wire to be low enough so that varying load impedance cannot change frequency response more than is acceptable.
Another issue involving load impedance and amplifiers is stability.
Certain impedances can cause an amplifier to go unstable.
This has to do with how conservative the amplifier is designed (phase margin).
You can design your crossover with conjugates so that you speaker has a flat impedance curve if you want to avoid the effects of varying load impedance upon your amplifier but the additional crossover components increase cost and complexity.

Daryl"

Always remember that snake oil salesmen will misrepresent anything that they possibly can to give themselves an advantage in getting your money.

Jim
 
Last edited:

fpitas

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The irony here is that a modern amp like an NCORE controls the speaker immensely better than any tube amp ever did. Either this man is badly confused, or he's selling oil of serpent.
 

fpitas

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He's selling tube amps, that's why he tries to discredit other topologies.
Doubtless that's just a coincidence. ;)
 

ppataki

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This was posted at Parts Express Techtalk about 16 years ago. It may help you.

"My guess is you are being lead astray by B.S.
Back EMF is a concept you learn in the beginning stages of electronics.
It is used to explain how devices such as inductors, motors, speaker drivers or any electromagnetic device can impede the flow of electricity.
A motor, speaker or inductors coil may have given resistance but apply a given voltage and less current flows than ohms law would predict at certain times.
Current is slow to start in the inductor, when the speakers diaphram moves it impedes the flow of current and same with the motors shaft.
The explaination is that the device generates it's own voltage in opposition to the applied voltage and that is why less current flows (because their is effectively less voltage applied to the circuit applied EMF - back EMF).
All fine and good.
That is the last you should hear or think about back EMF.
Moving on to the next level of electronics you move on to measuring impedance vs. frequency.
A motor operates at DC so you don't measure it's impedance vs. frequency but understand that it's impedance rises in proportion to it's shafts angular velocity.
An inductor has an impedance that increases with increasing frequency due to it's back EMF.
A speaker driver has an impedance curve with a resonant peak at Fs and rising impedance at high frequency due to voice coil inductance.
You probably have noticed that there are some 'experts' about who are trying to analize a system by following the signal through a system from the amplifier through a crossover to the driver and following back EMF from the driver back to the amplifier.
This is the scientific equivilant to chasing your tail.
Any time you see someone attempting this you can immediately ignore them as they are talking of things way over their head.
To calculate how a driver interacts with a circuit and amplifier you measure it's impedance and then solve the system as a circuit.
You can also model a driver rather than measure it's impedance by substituting an equivilant circuit like this simplified one shown below and then solve the whole thing (you can get more detailed with your equivilant circuit depending upon your needs).
Impedance fully describes back EMF and separate consideration need be given to back EMF.
In fact you cannot consider back EMF separately.
Back EMF has no place outside of beginning electronics.
Once you go beyond that you always use impedance vs. frequency.
So what you have is a drivers impedance and how the amplifier handles it.
Damping factor is a laymans term for output impedance.
The lower an amplifiers output impedance (higher damping factor) the less the ouput will be effected by varying load impedance.
Of course you have to remember that the loop impedance of your speaker wire adds to you amplifiers output impedance and is probably several times greater.
You want the combined output impedance of your amplifier and speaker wire to be low enough so that varying load impedance cannot change frequency response more than is acceptable.
Another issue involving load impedance and amplifiers is stability.
Certain impedances can cause an amplifier to go unstable.
This has to do with how conservative the amplifier is designed (phase margin).
You can design your crossover with conjugates so that you speaker has a flat impedance curve if you want to avoid the effects of varying load impedance upon your amplifier but the additional crossover componets increase cost and complexity.
Daryl"

Always remember that snake oil salesmen will misrepresent anything that they possibly can to give themselves an advantage in getting your money.

Jim

Maybe a bit off-topic but how much damping factor actually matters?
I mean let's assume that we have a value above 50; will there be an audible difference when listening to an amp with a value of 200 vs 2000?
(I know that according to Toole it won't matter above 25 or something, do not remember the exact figure he wrote in his book)
Many thanks
 

DonH56

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fpitas

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Maybe a bit off-topic but how much damping factor actually matters?
I mean let's assume that we have a value above 50; will there be an audible difference when listening to an amp with a value of 200 vs 2000?
(I know that according to Toole it won't matter above 25 or something, do not remember the exact figure he wrote in his book)
Many thanks
I've seen some manufacturers argue a value more like 100 - 200 is in order, using the example of speakers that have very low impedance at some frequencies. Of course their amps had incredible damping factor. Usually though, 25 is enough.
 

Gorgonzola

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This was posted at Parts Express Techtalk about 16 years ago. It may help you.

"My guess is you are being lead astray by B.S.
Back EMF is a concept you learn in the beginning stages of electronics.
It is used to explain how devices such as inductors, motors, speaker drivers or any electromagnetic device can impede the flow of electricity.
A motor, speaker or inductors coil may have given resistance but apply a given voltage and less current flows than ohms law would predict at certain times.
Current is slow to start in the inductor, when the speakers diaphragm moves it impedes the flow of current and same with the motors shaft.
The explanation is that the device generates it's own voltage in opposition to the applied voltage and that is why less current flows (because their is effectively less voltage applied to the circuit applied EMF - back EMF).
All fine and good.
That is the last you should hear or think about back EMF.
Moving on to the next level of electronics you move on to measuring impedance vs. frequency.
A motor operates at DC so you don't measure it's impedance vs. frequency but understand that it's impedance rises in proportion to it's shafts angular velocity.
An inductor has an impedance that increases with increasing frequency due to it's back EMF.
A speaker driver has an impedance curve with a resonant peak at Fs and rising impedance at high frequency due to voice coil inductance.
You probably have noticed that there are some 'experts' about who are trying to analyze a system by following the signal through a system from the amplifier through a crossover to the driver and following back EMF from the driver back to the amplifier.
This is the scientific equivalent to chasing your tail.
Any time you see someone attempting this you can immediately ignore them as they are talking of things way over their head.
To calculate how a driver interacts with a circuit and amplifier you measure its impedance and then solve the system as a circuit.
You can also model a driver rather than measure its impedance by substituting an equivilant circuit like this simplified one shown below and then solve the whole thing (you can get more detailed with your equivilant circuit depending upon your needs).
Impedance fully describes back EMF and separate consideration need not be given to back EMF.
In fact you cannot consider back EMF separately.
Back EMF has no place outside of beginning electronics.
Once you go beyond that you always use impedance vs. frequency.
So what you have is a drivers impedance and how the amplifier handles it.
Damping factor is a layman's term for output impedance.
The lower an amplifiers output impedance (higher damping factor) the less the output will be effected by varying load impedance.
Of course you have to remember that the loop impedance of your speaker wire adds to you amplifiers output impedance and is probably several times greater.
You want the combined output impedance of your amplifier and speaker wire to be low enough so that varying load impedance cannot change frequency response more than is acceptable.
Another issue involving load impedance and amplifiers is stability.
Certain impedances can cause an amplifier to go unstable.
This has to do with how conservative the amplifier is designed (phase margin).
You can design your crossover with conjugates so that you speaker has a flat impedance curve if you want to avoid the effects of varying load impedance upon your amplifier but the additional crossover components increase cost and complexity.

Daryl"

Always remember that snake oil salesmen will misrepresent anything that they possibly can to give themselves an advantage in getting your money.
Quoting the above ... "Damping factor is a layman's term for output impedance.
The lower an amplifiers output impedance (higher damping factor) the less the output will be effected by varying load impedance."

Ha! This is the specification for the Purifi 1ET400A amplifier output impedance: <65µO @ 1kHz. Yes, that's microohms. The 'damping factor' is close enough to infinite as to hardly matter.
 

egellings

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A modern feedback type class A or AB S.S. amp has an extremely low output impedance, some with a few milliohms or so. Any speaker's back EMF facing a pair of output terminals from an amplifier like that will quickly be shunted to AC ground through an impedance that low. A tube amp's output may get bounced around more due to the much higher output impedance.
 
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